Heavy duty pneumatic tire and manufacturing method thereof

Abstract

A tire 2 includes a tread 4 on which at least three circumferential grooves 24 continuously extending in a circumferential direction are formed, and a belt 14 located radially inward of the tread 4. A ratio of a center stretch, at a center portion of the belt, indicated by the follow/Mg formula (2) to a shoulder stretch, at an end portion of the belt, indicated by the following formula (1) is not less than 1 and not greater than 3, and the shoulder stretch is not less than 1%.(Shoulder stretch)100×(Rsa−Rsb)/Rsb  (1)(Center stretch)100×(Rca−Rcb)/Rcb  (2)

1 . A heavy duty pneumatic tire formed by vulcanizing and molding an uncured tire, the heavy duty pneumatic tire comprising:
 a tread that comes into contact with a road surface; and   a belt located radially inward of the tread, wherein   the tread has a tread surface having a profile that is convex radially outward,   the tread surface includes a crown portion including an equator of the tire, and a pair of side portions located outward of the crown portion in an axial direction,   a profile of the crown portion is represented by a circular arc having a radius Rc, and a profile of each of the side portions is represented by a circular arc having a radius Rs,   at least three circumferential grooves are formed on the tread, thereby forming at least four land portions aligned in the axial direction, and, among these land portions, a land portion located at an inner side in the axial direction is a center land portion, and a land portion located at an outer side in the axial direction is a shoulder land portion,   the belt includes a plurality of layers stacked in a radial direction, and each of the layers incudes a large number of belt cords tilted relative to a circumferential direction,   among the plurality of layers, a layer having a largest width in the axial direction is a first reference layer, a layer stacked at an outer side of the first reference layer is a second reference layer, and a layer located at an innermost side in the radial direction is a third reference layer,   a ratio of a center stretch Sc, at a center portion of the third reference layer, indicated by the following formula (2) to a shoulder stretch Ss, at an end portion of the third reference layer, indicated by the following formula (1) is not less than 1 and not greater than 3, and the shoulder stretch Ss is not less than 1%,   (shoulder stretch Ss)
   100×( Rsa−Rsb )/ Rsb   (1),
 
   (center stretch Sc)
   100×( Rca−Rcb )/ Rcb   (2),
 
   
       where Rsa is an inner diameter of the end portion of the third reference layer in the tire, Rsb is an inner diameter of the end portion of the third reference layer in the uncured tire, Rca is an inner diameter of the center portion of the third reference layer in the tire, and Rcb is an inner diameter of the center portion of the third reference layer in the uncured tire. 
     
     
         2 . The heavy duty pneumatic tire according to  claim 1 , wherein
 the at least three circumferential grooves include a center circumferential groove located at the inner side in the axial direction, and a shoulder circumferential groove located at the outer side in the axial direction, and   the shoulder circumferential groove is narrower than the center circumferential groove.   
     
     
         3 . The heavy duty pneumatic tire according to  claim 1 , wherein the shoulder stretch Ss is not greater than 2%. 
     
     
         4 . The heavy duty pneumatic tire according to  claim 1 , wherein
 an overall value of a radial runout at the center portion of the tread is not greater than 1.5 mm, and   an overall value of a radial runout at the shoulder portion of the tread is not greater than 1.5 mm.   
     
     
         5 . The heavy duty pneumatic tire according to  claim 4 , wherein an absolute value of a difference between the overall value of the radial runout at the center portion and the overall value of the radial runout at the shoulder portion is not greater than 0.5 mm. 
     
     
         6 . The heavy duty pneumatic tire according to  claim 4 , wherein the absolute value of the difference between the radial runout at the center portion and the radial runout at the shoulder portion at each portion in the circumferential direction of the tread is not greater than 0.20 mm. 
     
     
         7 . The heavy duty pneumatic tire according to  claim 1 , wherein the shoulder land portion continuously extends in the circumferential direction without interruption. 
     
     
         8 . The heavy duty pneumatic tire according to  claim 1 , further comprising a narrow land portion located outward of the shoulder land portion in the axial direction and extending in the circumferential direction, wherein
 a narrow circumferential groove is present between the narrow land portion and the shoulder land portion, and   the narrow circumferential groove is located outward of an end of the first reference layer in the axial direction.   
     
     
         9 . The heavy duty pneumatic tire according to  claim 1 , wherein a width in the axial direction of the first reference layer is equal to a width in the axial direction of the tread surface or smaller than the width in the axial direction of the tread surface. 
     
     
         10 . The heavy duty pneumatic tire according to  claim 1 , wherein an actual width of the shoulder land portion is larger than an actual width of the center land portion. 
     
     
         11 . The heavy duty pneumatic tire according to  claim 1 , wherein, in the first reference layer, a tilt angle of each of the belt cords at a layer end portion is equal to a tilt angle of each of the belt cords at an equator plane. 
     
     
         12 . The heavy duty pneumatic tire according to  claim 1 , wherein, in the first reference layer and the second reference layer, the tilt angle of each of the belt cords at the equator plane is not less than 12° and not greater than 20°. 
     
     
         13 . The heavy duty pneumatic tire according to  claim 1 , wherein a thickness of the tire measured along a line normal to an inner surface of the tire and passing through an end of the tread surface is larger than a thickness of the tire measured along the equator plane. 
     
     
         14 . The heavy duty pneumatic tire according to  claim 1 , wherein the radius Rs of the circular arc representing the profile of each of the side portions is larger than the radius Rc of the circular arc representing the profile of the crown portion. 
     
     
         15 . A method for manufacturing a heavy duty pneumatic tire including a tread that comes into contact with a road surface and a belt located radially inward of the tread, using a vulcanizing apparatus including a mold for molding the tire, the method comprising:
 a step of preparing an uncured tire including the tread and the belt;   a step of putting the uncured tire into the mold; and   a step of expanding the uncured tire in diameter and pressurizing and heating the uncured tire in the mold, wherein   the belt includes a plurality of layers stacked in a radial direction, and, among the plurality of layers, a layer having a largest width in an axial direction is a first reference layer, a layer stacked at an outer side of the first reference layer is a second reference layer, and a layer located at an innermost side in the radial direction is a third reference layer,   a ratio of a center stretch Sc, at a center portion of the third reference layer, indicated by the following formula (2) to a shoulder stretch Ss, at an end portion of the third reference layer, indicated by the following formula (1) is not less than 1 and not greater than 3, and   the shoulder stretch Ss is not less than 1%,   (shoulder stretch Ss)
   100×( Rsa−Rsb )/ Rsb   (1),
 
   (center stretch Sc)
   100×( Rca−Rcb )/ Rcb   (2),
 
   
       where Rsa is an inner diameter of the end portion of the third reference layer in the tire, Rsb is an inner diameter of the end portion of the third reference layer in the uncured tire, Rca is an inner diameter of the center portion of the third reference layer in the tire, and Rcb is an inner diameter of the center portion of the third reference layer in the uncured tire.